DESCRIPTION (adapted from Abstract): Microsporidiosis is now recognized as an important opportunistic pathogen especially in the setting of infection with human immunodeficiency virus (HIV). Enterocytozoon bieneusi and Septata intestinalis have been associated with diarrhea and wasting syndrome. S. intestinalis, Encephalitozoon hellem, and Enc. cuniculi have been associated with sinusitis, keratoconjunctivitis, and disseminated disease. The Principal Investigator and his colleagues have been working on the antigenic structure and molecular biology of the microsporidia for several years. They have cloned the rRNA genes from these organisms and developed non-invasive diagnostic probes using polymerase chain reaction (PCR), recognizing that all of the microsporidia infect host cells by using a polar tube. Recently, these researchers have identified monoclonal antibodies (Mab's) reacting with microsporidian polar tube. The Investigator now plans to clone the gene for polar tube protein (PTP); given the unique structural and biochemical properties of polar tubes, he speculates that polar tube proteins are conserved among the microsporidia and that the study of these proteins may yield novel targets for drug action. Because albendazole has been reported to be active against microsporidia, apparently by binding to beta-tubulin, the Investigator and his colleagues will clone the tubulin genes from several microsporidia and to explore the molecular biology of the Microsporidia genome by studying the genomic and cDNA clones of tubulin of these organisms. In addition, the researchers will continue the studies on diagnostic probes for the microsporidia. They will examine the Mab libraries for common and specific Mab's that may prove useful in diagnosis, and determine the diagnostic utility of in situ hybridization on stool with fluorescent- labeled oligomers to rRNA genes.